Point. - Here, all of the particles will originate at a single point. Changing the parameters here will move this generation point. Originally, this point will be at the center of the env_particles_custom entity in WC. Only the first three parameters will affect this shape. The first parameter will shift the point in the x-direction, the second in the y-direction, and the third in the z-direction. All parameter numbers correspond to the number of WC grid units.
Box - All of the particles spawn at a random point within a box. Changing the parameters will change the size of the box. The first and fourth parameters are the limits of the of the box along the x-axis, the second and fifth parameters are the limits of the box along the y-axis, and the third and sixth are the limits of the box along the z-axis. All numbers are relative to the center of the env_particles_custom entity. For instance, a third and sixth parameter of 32 and 64 respectively would result in all particles being generated between 32 and 64 units above the location of the env_particles_custom entity.
Sphere - This shape apparently does not work as of NSTR2.
Blob - This shape also apparently does not work as of NSTR2.